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#include "silk_SigProc_FIX.h" | |
/* Approximation of 2^() (very close inverse of silk_lin2log()) */ | |
/* Convert input to a linear scale */ | |
opus_int32 silk_log2lin( const opus_int32 inLog_Q7 ) /* I: Input on log scale */ | |
{ | |
opus_int32 out, frac_Q7; | |
if( inLog_Q7 < 0 ) { | |
return 0; | |
} | |
out = SKP_LSHIFT( 1, SKP_RSHIFT( inLog_Q7, 7 ) ); | |
frac_Q7 = inLog_Q7 & 0x7F; | |
if( inLog_Q7 < 2048 ) { | |
/* Piece-wise parabolic approximation */ | |
out = SKP_ADD_RSHIFT( out, SKP_MUL( out, SKP_SMLAWB( frac_Q7, SKP_MUL( frac_Q7, 128 - frac_Q7 ), -174 ) ), 7 ); | |
} else { | |
/* Piece-wise parabolic approximation */ | |
out = SKP_MLA( out, SKP_RSHIFT( out, 7 ), SKP_SMLAWB( frac_Q7, SKP_MUL( frac_Q7, 128 - frac_Q7 ), -174 ) ); | |
} | |
return out; | |
} |